This invention relates to the testing, such as for size, opens and shorts, of electrical traces, such as on a substrate such as a circuit board, and more specifically relates to a method using the photo-electric effect wherein the trace is not physically contacted.
In the current manufacture of electronic components, the packing density has increased considerably, resulting in traces of extremely small size. Fabrication of such traces is difficult such that defects are more common. Therefore, testing the quality of fine traces has become increasingly more important.
Most conventional methods of trace testing involve physically contacting the trace with one or two test probes. The physical placement accuracy of test probes limit their use in testing in mass. Many current traces are so small or densely packed that they can only be contacted with a physical probe individually with a very time consuming and uneconomical visual process.
Therefore, there has been a need for a test method for fine traces in which the trace is not physically contacted and which is not unduly time consuming.
This invention is a tester for testing an electrical trace without electrical connection to the test trace and it generally comprises an electro-magnetic source, such as a laser for providing a beam of electro-magnetic radiation directed on a single test trace for producing a photo-electric effect on the test trace liberating electrons from the trace, a collector disposed near the trace for collecting liberated electrons, and a collector circuit electrically connected to the collector for supplying a positive potential thereto and including a meter for measuring the photoelectric current to the collector from the trace. Preferably, the collector is a wire grid or a transparent sheet including a surface facing the test trace having a thin metal film thereon. In a preferred embodiment, trace and collected are placed in a vacuum chamber.
The method comprises directing an electro-magnetic beam on the test trace for producing a photo-electric effect on the test trace, liberating electrons from the trace, disposing a collector near the trace for collecting electrons liberated by the photo-electric effect on the trace, supplying a positive potential to the collector, and measuring the photoelectric current to the collector from the trace.
Other features and many attendant advantages of the invention will become more apparent upon a reading of the following detailed description together with the drawings in which like reference numerals refer to like parts throughout.